This invention relates to an apparatus for an elevator by controlling an induction motor for hoisting an elevator car by a variable frequency alternating current. More particularly, it relates to an apparatus for operating an elevator by providing a stable performance of the induction drive motor for the elevator even if the circuit constants of the motor vary.
A semiconductor technique has been recently developed, to increase the capacity of a power converter having inverters. Thus, it has been proposed to control an elevator hoisting induction motor by a variable frequency semiconductor power converter. There are various known systems for controlling the induction motor by a power converter, and a system for controlling an induction motor as a D-C motor equivalently in rotary coordinates by resolving the primary winding current into an exciting current component and a torque current component and treating the components as D-C values has been proposed.
An example of this system is shown in FIG. 1. The principle of operation of the control system shown in FIG. 1 will be first described.
A basic equation of an induction motor is represented as the following equation in a coordinate system of an ordinate axis d--an abscissa axis q rotating at the same angular velocity .omega. as a secondary winding crossing magnetic flux. In this equation, the phase of the axis d coincides with that of a secondary winding crossing magnetic flux vector. ##EQU1## In the above equation, Vd.sub.1 : the component of a primary voltage in axis d
Vq.sub.1 : the component of a primary voltage in axis q PA1 Id.sub.1 : the component of a primary current in axis d PA1 Id.sub.2 : the component of a secondary current in axis d PA1 Iq.sub.2 : the component of a secondary current in axis q PA1 Iq.sub.1 : the component of a primary current in axis q PA1 R.sub.1 : the resistance of a primary winding PA1 R.sub.2 : the resistance of a secondary winding PA1 L.sub.1 : self inductance of a primary winding PA1 L.sub.2 : self inductance of a secondary winding PA1 M: mutual inductance between primary winding and secondary winding PA1 P: differentiating operator (d/dt) PA1 p: the number of paired poles PA1 .omega..sub.r : mechanical angular velocity of a rotor PA1 .omega.: angular velocity of a rotary magnetic field
Since the axis d is selected as the axis of the secondary winding magnetic flux, the secondary winding magnetic flux of axis q is zero. Therefore, EQU Miq.sub.1 +L.sub.2 iq.sub.2 =0 (2)
From the second line of the equation (1) and the equation (2), EQU R.sub.2 Id.sub.2 +P(MId.sub.1 +L.sub.2 Id.sub.2)=R.sub.2 Id.sub.2 +P.PHI..sub.2 =0 (3)
In the equation (3), EQU .PHI..sub.2 =MId.sub.1 +L.sub.2 Id.sub.2 ( 4)
where .PHI..sub.2 represents the magnetic flux crossing the secondary winding.
From the equations (3) and (4), when the component Id.sub.2 of the secondary winding current in the d axis is cancelled, the following equation (5) can be obtained. ##EQU2##
Then, the following equation (6) can be obtained from the third line of the equation (1) and the equation (2). ##EQU3## If there is .omega..sub.s =.omega.-P.omega..sub.r (slip angle frequency), ##EQU4##
The above description is the principle of the control system shown in FIG. 1.
Next the control system in FIG. 1 will be described. In FIG. 1, numeral 1 designates a sinusoidal wave inverter for supplying voltages Vu, Vv and Vw to a hoisting induction motor 2 in accordance with voltage commands Vu*, Vv* and Vw*, respectively, numeral 3 designates a tachometer generator for detecting the rotating angular velocity .omega..sub.r of the motor 2, numerals 4a, 4b, 4c designate current transformers for detecting currents of phases U, V and W of the motor 2 which output detected current values Iu, Iv and Iw, respectively, and numeral 5 designates a coordinate converter for converting the detected 3-phase current values Iu, Iv and Iw into orthogonal biaxial currents Id.sub.1, Iq.sub.1 which outputs the components Id.sub.1 and Iq.sub.1 of the primary winding currents in the axes d and q represented by the following equation (8). ##EQU5## In the equation (8), cos .theta. and sin .theta. are output signals of a function generator 11 to be described later, and the components Id.sub.1 and Iq.sub.1 of the primary winding current in the axes d and q become D-C quantities by this conversion.
Numeral 6 designates a primary delay circuit for simulating the calculation of the equation (5), which comprises a subtractor 6a, a circuit 6b formed of a transfer function 1/s and a circuit 6c formed of a transfer function R.sub.2 /L.sub.2.
The output of the circuit 6b becomes as follows: ##EQU6## This output is equivalent to L.sub.2 .PHI..sub.2 /R.sub.2 M in the equation (5).
Numeral 7 designates a divider which divides the component Iq.sub.1 of the output of the converter 5 in the axis q by the output L.sub.2 .PHI..sub.2 /R.sub.2 M of the circuit 6b to calculate the slip angle frequency .omega..sub.s given by the equation (7). Numeral 8 designates a circuit of a transfer function p for converting the mechanical angular velocity .omega..sub.r of the motor 2 into an electric angular velocity p.omega..sub.r. Numeral 9 designates an adder for adding the output .omega..sub.s of the divider 7 and the output p.omega..sub.r of the circuit (8) to output a primary current angular frequency .omega.=p.omega..sub.r +.omega..sub.s, and numeral 10 designates a circuit of a transfer function 1/S for calculating the phase .theta. of the primary winding current by integrating the primary winding current angular frequency .omega.. Numeral 11 designates a function generator which outputs a cosine wave signal cos .theta. and a sinusoidal wave signal sin .theta. on the basis of the phase .theta. . Numeral 12 designates an exciting current instructing unit for outputting an exciting current command value .PHI..sub.2 */M corresponding to the secondary winding crossing magnetic flux command value .PHI..sub.2 *, numeral 13 designates a subtractor for subtracting the command value .PHI..sub.2 */M by the output .PHI..sub.2 /M of the circuit 6c, numeral 14 designates a circuit of a transfer function G.sub.1 for calculating the d-axis primary winding current command value Id.sub.1 * on the basis of a deviation (.PHI..sub.2 *-.PHI..sub.2)/M, numeral 15 designates a subtractor for subtracting the d-axis primary winding current command value Id.sub.1 * by the output signal Id.sub.1 of the converter 5, numeral 16 designates a circuit of a transfer function G.sub.2 for calculating the d-axis primary voltage command value Vd.sub.1 * on the basis of a deviation (Id.sub.1 *-Id.sub.1), numeral 17 designates a speed instructing unit for outputting the running speed command value .omega..sub.r * of an elevator, numeral 18 designates a subtractor for subtracting the speed command value .omega..sub.r * by the output signal .omega..sub. r of the generator 3, numeral 19 designates a circuit of a transfer function G.sub.3 for calculating the q-axis primary winding current command value Iq.sub.1 * on the basis of a deviation (.omega..sub.r *-.omega..sub.r), numeral 20 designates a subtractor for subtracting the q-axis primary winding current command value Iq.sub.1 * by the output signal Iq.sub.1 of the converter 5, numeral 21 designates a circuit of a transfer function G.sub.4 for calculating the q-axis primary winding voltage command value Vq.sub.1 * on the basis of a deviation (Iq.sub.1 *-Iq.sub.1), and numeral 22 designates a coordinate converter which converts orthogonal biaxial voltages Vd.sub.1 *, Vq.sub.1 * into 3-phase A-C voltage command values Vu*, Vv*, Vw*, respectively by the following equation (9). ##EQU7## Numeral 23 designates a sheave coupled directly with the motor 2, numeral 24 designates a deflecting sheave, numeral 25 designates a rope, numeral 26 designates an elevator car, and numeral 27 designates a counterweight.
The torque generated by the motor 2 is represented as follows by the secondary crossing magnetic flux .PHI..sub.2 and the q-axis secondary winding current iq.sub.2. EQU T=-p.PHI..sub.2 iq.sub.2 ( 10)
The equation (10) can be modified as the following equation (11) by the equations (2) and (7). ##EQU8## As apparent from the equation (11), the torque T generated by the motor 2 becomes a function of the resistance value R.sub.2 of the secondary winding, the resistance value R.sub.2 depends upon the temperature, and when the motor 2 is operated with a load for a long period of time, the temperature of the secondary winding rises, thereby causing the resistance value R.sub.2 to increase. Therefore, when the resistance value R.sub.2 used for the calculation of the circuit 6c is assumed to be constant and the motor 2 is controlled accordingly, since the actual value of the resistance R.sub.2 varies due to the temperature rise, errors in the calculating equations described above increase, and the smooth rise of the elevator car cannot be obtained.